DHEA or dehydroepiandrosterone is a natural steroid produced essentially by the corticoadrenal glands. Exogenous DHEA, administered topically or orally, is known for its ability to promote keratinization of the epidermis (JP-07 196 467) and to treat dry skin by increasing the endogenous production and secretion of sebum, thus strengthening the barrier effect of the skin (U.S. Pat. No. 4,496,556). It has also been disclosed, in U.S. Pat. No. 5,843,932, to use DHEA for curing atrophy of the dermis by inhibition of the loss of collagen and of connective tissue. Finally, the ability of DHEA to control the papery appearance of the skin (FR 00/00349), to adjust the pigmentation of the skin and hair (FR 99/12773) and to combat atrophy of the epidermis (FR 00/06154) has been demonstrated. These properties of DHEA make it a candidate of choice as an antiageing active principle.
However, DHEA exhibits effects of a hormonal nature which can render its use problematic.
For this reason, attempts have been made to make available DHEA derivatives which exhibit similar advantageous properties to DHEA but which do not have hormonal effects.
DHEA derivatives already known include 3β-acetoxy-7-oxo-DHEA or Δ5-androstene-3β-acetoxy-7,17-dione, which has been disclosed as being effective in the modulation of the immune system (U.S. Pat. No. 5,292,730, U.S. Pat. No. 5,585,371, U.S. Pat. No. 5,641,766), the treatment of Alzheimer's disease (U.S. Pat. No. 5,707,983), the treatment of HIV syndrome (U.S. Pat. No. 5,885,977) and for promoting weight loss (U.S. Pat. No. 5,296,481, U.S. Pat. No. 5,807,848).
PCT patent application WO 99/25333 additionally mentions the use, in particular the topical use, of 3β-acetoxy-7-oxo-DHEA in the prophylactic and curative treatment of lupus erythematosus, which is a disorder of the immune system capable of affecting several organs and which is revealed in the skin by a transverse redness of the face and/or by squamous erythemal plaques disseminated over the body.
U.S. Pat. No. 5,424,463 discloses 7-keto-DHEA (or Δ5-androstene-3β-ol-7,17-dione) and its hydrolysable derivatives obtained by modification of the 3β-hydroxy group, the derivatives being capable of restoring 7-keto-DHEA after hydrolysis. The 3β-hydroxy group is converted to carbamate or is esterified with (i) a saturated or unsaturated and normal or branched C2-C22 aliphatic acid, (ii) a C7-C22 aromatic acid, (iii) a dicarboxylic acid comprising 3 or more carbon atoms, for which only one carbonyl group is esterified with the 3-hydroxy group of the steroid, or (iv) an inorganic acid, such as sulphuric acid and phosphoric acid. U.S. Pat. No. 5,424,463 discloses 7-keto-DHEA and its hydrolysable derivatives as being effective in promoting weight loss.
PCT patent application WO 98/40074 discloses the use of DHEA derivatives of formula (A): in which:                R1 is chosen from: a hydrogen atom or the following functional groups: ester of organic acid comprising 1 to 24 carbon atoms, sulphuric ester or phosphoric ester, or carbonaceous ether comprising 1 to 24 carbon atoms comprising no or several nitrogen atoms, or ethers of carbohydrates comprising 3 to 100 carbon atoms and their derivatives comprising or not comprising one or more nitrogen atoms;        R2 is chosen from: a hydrogen atom or an ester functional group of fatty acid comprising 1 to 24 carbon atoms;        R3 is chosen from: a hydrogen atom, an —OH group or groups of formulae: —CO—R4, —CHOH—R4, ═CH—CH3, ═COH—CH3, —CHR4—CH3 or ═O, in which groups R4 is an alkyl group comprising from 1 to 10 carbon atoms which is or is not substituted;in a composition for preventing or treating signs of cutaneous ageing and/or the effects of UV radiation on the skin.        
PCT patent application WO 00/28996 discloses a composition for improving the texture of tissues comprising a DHEA derivative of formula (A) in combination with an elastin-derived peptide obtained by selective cleavage of elastin by thermolysin.
However, to Applicants' knowledge, it has never been suggested to use DHEA derivatives of general formula (I) for improving the appearance of keratinous substances, in particular in the treatment of signs of ageing.